1. Field of the Invention
The present invention relates to a needle assembly for collecting fluid such as blood from a patient, and more particularly, concerns a needle assembly for collecting multiple samples of blood from a patient into evacuated tubes without leaking blood while the tubes are being changed, and with a provision for indicating the entry of the needle assembly into the vein of the patient.
2. Description of the Prior Art
It is now standard practice to collect multiple samples of fluid, such as blood, from a patient in a single procedure. Once the needle is inserted into the vein of the patient, successive evacuated blood collection tubes are inserted into a holder which is connected to the needle and is adapted to receive these evacuated tubes therein. As each filled tube is removed from the holder, the needle remains inserted into the patient's vein. Various valves are now in use which prevent blood from flowing out of the holder during the time between removal of the filled tube and insertion of the next evacuated tube for collection of the subsequent sample. Elastomeric sleeves over an interior needle commonly serve this valve purpose. It is appreciated that, while the known valves for multiple sample needle assemblies perform satisfactorily, different ways are being sought to provide improvements in these devices.
U.S. Pat. Nos. 4,166,450; 4,099,520; 3,557,778; and 3,528,404 disclose representative blood sampling devices through which the flow of blood can be controlled during the collection of multiple samples.
In addition, it is also desirable to provide a mechanism whereby the user of a multiple sample needle assembly can be informed when the intravenous needle has penetrated the vein of the patient. Many times in collecting blood from a patient it is difficult to locate the vein or for other reasons blood flow into the collection device is minimal. In these instances, it becomes most advantageous to be able to make a quick determination that entry into the vein has been made and that blood is flowing into the needle assembly. Once this determination has been made and vein entry indeed accomplished, the evacuated blood collection container can then be inserted into the collection assembly in accordance with these well known techniques of collecting multiple blood samples during a single collection procedure.
One of the problems which arises during the venipuncture step concerns the pocket of air which is found in various needle assemblies useful for multiple sample blood collections. When venipuncture is made, and the evacuated blood collection container is not yet attached to the opposite end of the needle structure, blood cannot always flow into the needle assembly because of this pocket of air, which, under normal atmospheric conditions, remains inside the needle assembly. Accordingly, even though vein entry may have been accomplished, the blood may not move through the intravenous needle into the collection assembly under tourniquet pressure until the evacuated blood collection container is attached, whereupon the vacuum source causes sufficient draw through the needle assembly. It is thus desirable to provide a mechanism for purging the air from inside the needle assembly so that blood can readily flow into the assembly as it displaces the air.